On Saturday, 7 March 2020 10:40:08 UTC, wrote:
Clive Arthur brought next idea :

Yes, it's a 'carbon pile rheostat' patented by Singer in 1949 - lots of
carbon discs in a tube and you lower the resistance by squeezing them
together. Google the phrase and there are some instructions on repairing
them.

I always had in mind to try to put together something better, like a
TRIAC control with speed feedback. On the rare occasions I have used
out machine, I found the sudden take off at speed awkward to control
and use. Someone must have tried such an improved design?

Of course, modern Berninas use proper control. But budget machines just used a resistor. The main difference it makes is at very low speeds, where a decent control has pretty much perfect control.


NT